Stainless steel

ABSTRACT

Stainless steel characterized by a combination of ductility and low work-harding rate, and containing carbon up to 0.15%, manganese 3% to 10%, phosphorus not exceeding 0.06% sulfur not exceeding 0.03% silicon 0.15% to 1%, chromium 15% to 19%, nickel 3.5% to 6%, copper 0.5% to 4%, nitrogen 0.04% to 0.4% with a nitrogen content of at least 0.07% for the maximum values of carbon, manganese and nickel, and a chromium content of about 19%, and remainder iron.

Paul M. Allen Middletown, Ohio Sept. 20, 1968 Oct. 26, 197 1 Armco Steel Corporation Middletown, Ohio Continuation-impart of application Ser. No. 305,533, Aug. 29, 1963, now abandoned. This application Sept. 20, 1968, Ser. No. 761,346

[72] Inventor [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] STAlNLlESS STEEL Primary Exnminen-Hyland Bizot Attorney-John Howard Joynt ABSTRACT: Stainless steel characterized by a combination of ductility and low work-harding rate, and containing carbon up to 0.15%, manganese 3% to 10%, phosphorus not exceeding 0.06% sulfur not exceeding 0.03% silicon 0.15% to 1%, chromium 15% to 19%, nickel 3.5% to 6%, copper 0.5% to 4%, nitrogen 0.04% to 0.4% with a nitrogen content of at least 0.07% for the maximum values of carbon, manganese and nickel, and a chromium content of about 19%, and remainder ll'On.

STAINLESS srnnr.

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of my copending application Ser. No. 305,533, filed Aug. 29, 1963 now abandoned and entitled Stainless Steel. In a sense the application is a companion to the then copending application Ser. No. 299,110, filed July 31, 1963 and entitled Stainless Steel and Articles," now U.S. Pat. No. 3,282,684 of Nov. 1, 1966.

One of the objects of the present invention is to provide a stainless steel which not only is comparatively inexpensive as to alloying ingredients but which works well in the hot mill, and in the cold mill as well, particularly permitting a short routing through the cold mill with maximum reductions without necessity for intermediate anneals, all with savings in mill costs.

A further object is the provision of hot-rolled sheet, wire and the like, and the provision of cold-rolled sheet, strip and the like, as well as cold-drawn wire and the like, all of which lend themselves to a variety of forming operations such as bending, pressing, spinning, drawing and deep-drawing, as well as various machining operations such as shearing, sawing, drilling and threading, and which sheet, strip, wire, and the like, whether hot-worked or cold-worked, readily may be welded, brazed or soldered in the fabrication of a variety of articles of ultimate use.

Other objects of my invention, and advantages incident thereto, will be apparent, or pointed to, in the description which follows.

My invention-will be seen to reside in the combination of elements and composition of ingredients forming the alloy steel of my invention, and in the products and articles fashioned of such steel, all as more particularly described herein, the scope of which invention is set out in the claims at the end of this specification.

BACKGROUND OF THE INVENTION As a guide to a better understanding of certain features of my invention, it may be noted here that at the present time there is a wide variety of stainless steels available to the art. The selection of any particular grade by the user largely depends upon the combination of characteristics sought, that is, mechanical properties, corrosion resistance, heat resistance, and the like. Now the type 430 stainless steel (carbon 0.12 percent max., manganese 1.00 percent max., silicon 1.00 percent max., phosphorus 0.04 percent max., sulphur 0.03 percent max., chromium 14.00 percent to 18.00 percent, and remainder iron) is well known and widely used. It is comparatively inexpensive. With an ultimate tensile strength of 75,000 p.s.i. a 2 percent yield strength of about 45,000 p.s.i., and a hardness of about Rockwell B80, it lends itself to common working and forming operations. Unfortunately, the corrosion-resistant properties of the steel are limited to environments which are only mildly corrosive. While heretofore used in the automotive industry, for body trim, wheel covers and other bright metal parts, eye appeal may be lost under the conditions encountered in use; corrosion, pitting, the development of a red rust, are encountered in salty atmosphere and especially as a result of the salt commonly used to deice the streets, roads and highways in wintertime.

The type 301 stainless steel (carbon 0.15 percent max., manganese 2.00 percent max., silicon 1.00 percent max., phosphorus 0.045 percent, sulphur 0.03 max., chromium 16.00 to 18.00 percent, nickel 6.00 to 8.00 percent, and remainder iron), of course, is well calculated to meet the demands of the automotive industry and other industries where bright metal is desired. In the annealed condition, cold-rolled sheet and strip has a tensile strength of about 110,000 p.s.i., a 0.2 percent yield strength of about 40,000 p.s.i., and a hardness of about Rockwell B85. This grade of stainless steel is costly, however, first because of the rather high alloy content, particularly the large amount of nickel used, and second,

because the steel is inclined to harden during working, that is, to harden as it is cold-rolled into sheet, strip and the like or cold-drawn into wire. In these operations intermediate annealing of the metal is necessary. And it will be appreciated that the intermediate annealing steps are both time-consuming and costly.

The type 302 grade of stainless steel (carbon 0.15 percent max., manganese 2.00 percent max., silicon 1.00 percent max., phosphorus 0.045 percent max., sulphur 0.03 percent max., chromium 17.00 to 19.00 percent, nickel 8.00 to 10.00 percent, and remainder iron) works well in the mill and readily is cold-rolled into sheet and strip, and is readily cold-drawn into wire. And its mechanical properties are about the same as the type 301, being perhaps a bit more ductile; in the annealed condition, cold-rolled sheet and strip has a tensile strength of about 90,000 p.s.i., a yield strength of 40,000 p.s.i. and a hardness of about Rockwell B85. But this steel is even more expensive than the type 301; the ingot cost is high because of the significantly higher chromium content and the much higher nickel content.

The type 201 stainless steel (carbon 0.15 percent max., manganese 5.5 to 7.50 percent, silicon 1.00 percent max., phosphorus 0.060 percent max., sulphur 0.030 percent max., chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, nitrogen 0.25 percent max., andre'mainder iron), is less expensive in the ingot than the type 3011. But this steel (tensile strength 115,000 p.s.i., yield strength 55,000 p.s.i. and hardness Rockwell B90) is inclined to even more rapid workhardening than type 301 with resultant high-mill cost in the production of cold-rolled sheet, strip, and the like, and colddrawn wire, particularly because of the necessity for intermediate annealing in achieving the desired final reduction. While a similar grade, the type 202 (carbon 0.15 percent max., manganese 7.5 to 10.00 percent, silicon 1.00 percent max., phosphorus 0.060 percent max., sulphur 0.030 percent max., chramium 17 to 19 percent, nickel 4 to 6 percent, nitrogen 0.25 percent max., and remainder iron) with tensile strength 105,000 p.s.i., yield strength 55,00 p.s.i. and hardness Rockwell B90 in annealed condition, is possessed of a lower work-hardening rate and consequently works in the cold mill at lower cost than the type 201, the steel is even more expensive in the ingot than the type 201 because of the significantly larger quantities of chromium and increased nickel and manganese.

While there are other stainless steels which lend themselves to cold-rolling and cold-drawing without necessity for inter mediate annealing and consequent increased cost of coldreduction, they fall short of the requirements of the art, either being too costly in the ingot or lacking in desired complement of mechanical properties and corrosion-resisting properties. While, for example, the chromium-nickel-copper stainless steel described in the Bloom-Clarke US. Pat. No. 2,687,955, Aug. 31, 1954, entitled Cold-workable Stainless Steel and Articles, is possessed of a comparatively low work-hardening rate and well lends itself to the production of cold-rolled sheet and strip and cold-drawn wire at minimum cost, it, too, is comparatively expensive. Moreover, the combination of mechanical properties and corrosion-resisting properties of that steel is such that its field of usefulness is rather limited; it is not suited to the production of articles of ultimate use where severe deep-drawing operations are required. The metal is inclined to local fracture because of inadequate uniform elongation.

Therefore, an object of the present invention is the provision of a stainless steel having good corrosion-resisting properties, which steel is less costly than those heretofore available in the art; which is produced in good quality, teems well and readily works down from ingot to billet, to bar stock and the like; and which steel is possessed of a low work-hardening rate, readily lending itself to cold-rolling into sheet and strip, particularly of thin sections, and cold-drawing into wire where reductions on the order of some 75 to percent are had, all without necessity for interruption in the cold-rolling or colddrawing operations by intermediate annealing, which sheet,

articles of ultimate use by a variety of working and forming operations.

SUMMARY OF THE INVENTION Turning now to the practice of my invention, I provide a stainless steel which, in general, is possessed of the complement of corrosion-resisting and mechanical properties characterizing the types 202 and 302 steels briefly discussed above. My steel enjoys the low cost of conversion into cold-rolled sheet and strip and cold-drawn wire characterizing the types 202 and 302; more significantly, however, it is much less costly than either of these types in the ingot because of the savings in the alloying ingredients. Actually, it is less costly than the types 201 and 301, especially in the cold-reduced condition.

My ,steel essentially consists of carbon up to 0.15 percent, manganese 3 to percent, silicon 0.15 to 1 percent, chromium to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.04 to 0.4 percent with a nitrogen content of at least 0.07 percent for the maximum values of carbon, manganese and nickel (or, more particularly, with a manganese content of about 10 percent) and a chromium content of about 19 percent, and remainder substantially all iron. The composition of the steel is viewed as being critical. Any substantial departure from the ranges set out above results in a disturbance of the composition balance with a resulting sacrifice of one or more of the desired characteristics.

More particularly, in my steel carbon is present in amounts up to 0.15 percent. Usually, I prefer at least 0.04 percent carbon because of its austenite-stabilizing effect. But no more than 0.15 percent can be tolerated because, as a result of chromium carbides appearing with the higher carbon content, the steel then becomes susceptible to intergranular corrosion during an acid-pickling operation. MOreover, an excess of carbon inclines to the development of a sensitized structure following a welding operation, with resultant loss of corrosion resistance. Usually, I prefer the somewhat lower carbon content of 0.04 to 0.11 percent, preferably 0.07 to 0.1 1 percent.

Manganese, likewise, is an essential ingredient, this amounting to at least 3 percent in order to assure, along with nickel, the desired austenitic structure. A manganese content in excess of the 10 percent figure, however, is not desired because, surprisingly enough, at hot-working'temperatures excessive manganese inclines to the introduction of ferrite with resultant risk of breakage in the hot mill. Moreover, excessive manganese becomes uneconomical, the melting losses become excessive. The manganese content of my steel, therefore, is in the amount of 3 to 10 percent, and preferably 5.5 to 7.5 percent, and even more preferably 5.5 to 6 percent. The best combination of desired properties and minimum cost are had with the most preferred range.

As to silicon, this ingredient is in the amount of at least 0.15 percent in order to assure clean metal, essentially free of oxide inclusions when made in the electric arc furnace or the induction furnace. Actually, I prefer a silicon content of at least 0.4 percent for best results. The silicon content desirably should not exceed 1 percent, however, and preferably should not exceed 0.75 pereent,because excessive silicon is inclined to introduce ferrite with resultant disturbance of the structural balance. And to compensate for that there would be a demand for more nickel, a particularly expensive alloying addition, as noted below. The silicon content of my steel, therefore, ranges from 0.15 to 1 percent, preferably 0.4 to 0.75 percent.

The chromium content of my steel is in the amount of 15 to 19 percent as noted above. Less than the 15 percent figure results in undesired loss of corrosion resistance. Actually, I prefer at least 16 percent chromium for full assurance of desired corrosiomresisting properties. The chromium content, however, should not exceed 19 percent, preferably not over 18 percent, because it inclines to the production of delta-ferrite at hot-working temperatures with resultant sacrifice in quality; the metal is inclined to break during the hot-working operation. While this tendency might be counteracted by an increase in nickel content it will be immediately recognized that this increase would defeat the object of the invention, that is, it would defeat the effort to provide a low-eost stainless steel. A chromium content of 16.25 to 17.25 percent gives best results.

The nickel content, too, is critical. At least 3.5 percent nickel is required to give a stably austenitic structure, with freedom from delta-ferrite. Moreover, with a nickel content lower than the 3.5 percent figure, the work-hardening rate becomes excessive. A nickel content exceeding the 6 percent figure, however, objectionably increases the cost of the steel and moreover results in a loss of strength. A nickel content of 3.5 to 4.5 percent, and even 3.5 to 5.5 percent, is preferred in order to assure the best combination of mechanical properties compatible with cost.

In my steel copper is an essential ingredient, this in the amount of 0.5 to 4 percent, preferably in the amount of l to 4 percent, and more preferably 1 to 3.5 percent. A copper con tent below the 1 percent figure, and certainly one below the 0.5 percent figure, affords little benefit; it fails to exert a sufficient effect on the work-hardeining rate of the steel. Actually, I prefer at least 1 percent copper in my steel in order to lower the work-hardening rate commonly encountered in the austenitic chromium-nickel-manganese steels. Copper in excess of the 4 percent figure is not acceptable, however, because I find this exceeds the limit of solubility. And with the excess there is likelihood of breakage in the hot mill; the metal is inclined to hot-shortness. Usually I prefer to maintain the copper content at a figure not exceeding 3.5 percent. Most preferably, the copper content is in the amount of 2.5 to 3.25 percent.

Nitrogen, too, is an essential ingredient and this in purposeful amount, that is, in the amount of 0.04 to 0.4 percent. Nitrogen helps to stabilize the metal, at least 0.04 percent being required for the purpose. I find, however, that with a chromium content exceeding about 18 percent, i.e. chromium about 19 percent, at least 0.07 percent nitrogen is required even with the austenite-forming ingredients carbon, manganese and nickel at the maximum amounts noted, namely, 0.15 percent, 10 percent and 6 percent respectively. Nltrogen, as noted, not only helps stabilize the metal but, even more importantly, decreases the work-hardening rate. Even better results, with substantial freedom from delta-ferrite, are had with a minimum nitrogen content of 0.05 percent with nitrogen amounting to at least 0.08 percent for a manganese content of about 10 percent and a chromium content of about 19 percent. Actually, I prefer a nitrogen content of at least 0.07 percent and preferably at least 0.08 percent in order to safely assure a freedom from the formation of delta-ferrite, with at least 0.10 percent nitrogen preferably being employed where the manganese content is about 10 percent and the chromium content about 19 percent. With a nitrogen content exceeding the 0.4 percent figure there is a possibility of unsoundness. 1 generally prefer an upper limit of 0.25 percent nitrogen, and more preferably 0.12 percent. The preferred nitrogen content is 0.07 to 0.12 percent, and for a best combination of results 0.08 to 0.12 percent.

In my steel it will be understood that phosphorus and sulphur commonly are present, these in usual amounts, namely, phosphorus not exceeding 0.06 percent, and sulphur not exceeding 0.03 percent. The remainder of the composition is substantially all iron.

DESCRIPTION OF THE PREFERRED EMBODIMENTS to 6 percent, copper 0.05 to 4 percent and preferably 0.75 to 2.5 percent, nitrogen 0.04 to 0.4 percent and preferably 0.05 percent to 0.1 percent with the minimum nitrogen content being 0.07 percent where the manganese content is about 10 percent and the chromium content about 19 percent. The remainder of the composition is substantially all iron. Even better results are had with a minimum nitrogen content of 0.05 percent, with at least 0.08 percent nitrogen being employed where the chromium content exceeds about 18 percent, notably about 19 percent, and manganese about 10 percent.

A somewhat more restricted composition to give substantial freedom from delta-ferrite is as follows: carbon up to 0.15 percent max. and preferably 0.04 to 0.1 1 percent, manganese 3 to 7.5 percent, phosphorus 0.06 percent mare, sulphur 0.03 percent rnax., silicon 0.15 to 1 percent and preferably 0.4 to 1 percent, chromium to 18 percent, nickel 3.5 to 5.5 percent, copper 0.5 to 4 percent and preferably 1 to 3.5 or 4 percent nitrogen 0.05 to 0.25 percent; preferably in order to safely assure a freedom from delta-ferrite the nitrogen is in the amount of 0.07 to 0.12 percent. Here again, the remainder of the composition is substantially all iron.

A preferred steel according to my invention is as follows: carbon 0.04 to 0.15 percent, preferably 0.04 to 0.1 1 percent, manganese 5.5 to 7.5 percent, phosphorus 0.06 percent max., sulphur 0.03 percent max,, silicon 0.4 to 1 percent, chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, copper 0.5 to 4 percent, preferably 1 to 3.5 percent, nitrogen 0.08 to 0.25 percent, preferably 0.08 to 0.12 percent, and remainder substantially all iron. A further referred steel analyzes about; carbon 0.07 to 0.1 1 percent, manganese 5.5 to 6 percent, phosphorus 0.06 percent max., sulfur 0.03 percent 111811., silicon 0.4 to 0.75 percent, chromium 16.25 to 17.25 percent, nickel 3.5 to 4.5 percent copper 2.5 to 3.25 percent, nitrogen 0.08 percent to 0.12 percent, and remainder substantially all iron.

One steel of my invention of higher chromium, nickel and manganese balance is of the composition: carbon up to about 0.15 percent, preferably 0.04 to 0.1 1 percent, manganese 7.5 to 10 percent, silicon 0.4 to 1 percent, chromium 17 to 19 percent, nickel 4 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.4 percent with a minimum nitrogen content of 0.08 percent for about 10 percent manganese and about 19 percent chromium. The remainder is substantially all iron.

The pronounced effect of the copper content on my chromium-nickel-manganese stainless steel is conveniently illustrated in tables 1(a) and 1(b) given below. In Table l (a) I present the chemical analysis of three chromium-nickel-manganese stainless steels, two according to my invention where copper is in the amount of 0.5 to 4 percent and one outside of my invention with copper present in but residual amounts. The comparative mechanical properties for the three steels, namely the strengths developed by drastic cold-deformation, are given in table l(b).

TABLE I(a).-OHEMICAL COMPOSITIONS Heat No. C Mn Si Cr Ni 011 N 1 Outside invention. Note.-Reznainder of the steel is substantially iron.

TABLE l(b) Strength at 65% Cold-Reduction for the Steels of Table 1(0) Heat No. 0.2% Y.S. k.s.i. U.T.S. 1t.$.i.

Outside invention.

Note that while the chromium-nickel stainless steel of residual copper content, but of significant carbon, silicon and nitrogen contents, develops a yield strength of 245.4 1(.s.i. (245,400 p.s.i.) and a tensile strength of274.l 14.5.1. (274,100 p.s.i.) with a cold-reduction of 65 percent, the two chromiumnickel-manganese stainless steels of my invention with copper contents of about 1.5 percent and 3 percent develop yield strengths of only 194.8 l(.s.i. and 176.3 l(.s.i. respectively, and tensile strengths ofonly 217.5 1(.s.i. and 196.5 l1(.s.i.

Steel according to my invention is conveniently melted in the electric arc furnace as suggested above. Where desired, however, it may be melted in the induction furnace or by other means. The furnace is tapped, the metal is teemed into ingot molds, and the metal is then processed from ingot into slabs, blooms and billets. The metal handles well in the furnace and ladle and works well in the hot mill. The slabs, blooms or billets are reheated and hot-rolled as in the production of sheet, strip, wire and the like. Here again, it works well; it may be brought down to a thickness of about 0. 100 inch.

The hot-rolled steel sheet and strip or hot-rolled wire is conveniently descaled, with or without a prior annealing, and then cold-reduced to size. No intermediate annealing is required with consequent extra handling and delay. Cold-rolling costs thus are at a minimum. And the extent of cold-reduction, particularly in the production of sheet and strip of thin sections, say 0.015 inch to 0.032 inch in thickness, is at least 60 percent and may amount to some 75 percent or more without intermediate anneal. Similarly, the cold-drawing of wire is had without intermediate annealing even though the extent of the draw amounts to as much as 75 percent or percent.

As particularly illustrative of the steel of my invention, especially the rate of work-hardening (gauged by the increases in tensile and yield strengths) as compared with that of the wellknown 18-8 chromium-nickel stainless steel, 1 give below in tables 11 (a) and 11 (b the chemical composition and mechanical properties of yield strength, tensile strength and elongation of some 14 steels according to my invention and two of the 18-8 steels.

TABLE 11(a) .CHEMICAL ANALYSES Heat No. 0 Mn Si Cr Ni Cu N 1 18-8 Cr-Ni steels of prior art. M R

The mechanical properties of the steels of table 11(0), particularly the 0.2 percent yield strength in kilopounds per square inch (1K.s.i.), the tensile strength, also in l(.s.i. the percent elongation in 2 inches and the Rockwell hardness in the annealed condition with zero cold-reduction and for a coldreduction of about 65 percent are given below in table ll(b), the samples of the 18-8 steels being of 0.048 inch strip and those of my steel being of 0.025 inch strip.

TABLE II(b) Mechanical properties of the steels of table II(a) for samples of zero reduction and samples of 65% reduction Percent Percent cold- 2% Y.S., U.'I.S., elong. Rockwell Heat No. reduction K s.i. K s.i. 1n 2" hardness 0 45. 1 98. 3 62. 5 5B 64. 3 186. 6 203. 3 3. 5 44. 0C 0 46. 8 100. 6 60. 0 81. 5B 64. 7 189. 6 209. 0 3. 0 44. 5C 0 49. 2 102. 7 57. 5 82. 5B 64. 6 184. 9 206. 1 5. 0 43. 5C 0 48. 3 99. 0 56. 5 82. 0B 64. 2 181. 2 198. 2 5. 0 42. 5C 0 53. 4 103. 0 52. 5 83. 0B 64. 6 176. 2 196. 6 4. 5 42. 0C 46. 9 98. 3 55. 5 81. 5B 64. 0 173. 6 192.1 4. 5 41. 5C 44. 9 98. 4 62. 0 76. 53 65.0 190. 5 205. 0 2.6 43. 5C 0 46. 9 100.8 62. 0 79. 0B 65. 0 184. 5 200. 3 3. 0 43. 5C 0 40. 2 97. 1 65. 5 76. 5B 65. 4 195. 0 204. 6 2. 5 43. 5C 40.6 94. 6 59. 0 75. 5B 65. 0 180. 7 195. 2 2. 5 42. 5C 40. 8 96. 4 60. 5 76. 0B 65 0 184.5 198. 0 3. 0 42. 0C 3313 2 0 40. 0 94. 9 62. 0 74. 5B 65. 0 171. 7 192. 0 3. 0 42. 00 3315 0 42. 7 96. 2 59. 0 76. 0B 65. 7 174. 5 193. 2 4. 0 41. 00 3320 0 46. 3 98.2 55. 0 79. 0B 64. 7 173. 2 188. 7 5. 5 41. 0C

1 18-8 Cr-Nl steels of prior art (Type 302). 2 Extrapolated from 60% reduction figures.

It is to be noted from the data presented above that the steels illustrative of my invention develop yield strengths and tensile strengths (indicative of work-hardening rates) which are no greater than those developed with the cold-working of the well-known l8-8 chromium-nickel stainless steel, hardening rates which are widely accepted in the art. Yet the cost is substantially lower because of the lower requirements of chromium and nickel, the nickel requirement being only about one-half of that necessary for the 18-8 steel. And actually, the work-hardening developed in my steel is a bit less than that developed in the 18-8 steel.

Thus, for example, the two 18-8 steels in annealed condition have yield strengths of 40 and 45.4 K.s.i. and tensile strengths of 89.1 and 90.1 K.s.i. As a result of cold-reduction in the amount of 65 percent there is an increase in both strengths; the yield strength of the two samples is raised to 185 and 197.2 K.s.i. and the tensile strengths to 202 and 210 K.s.i., respectively.

In my steels of the most preferred composition (Heats 3313-1, 3313-2, 3315 and 3320) yield strengths ranging from 40.0 to 46.3 K.s.i. and tensile strengths ranging from 94.9 to 98.2 K.s.i. are increased by cold-reduction in the amount of some 65 percent only to some 171.7 to 184.5 K.s.i. yield and some 188.7 to 198.0 K.s.i. tensile. It is noted that in my preferred steel the tensile strength is just about doubled as a result of the 65 percent cold-reduction, while in the 18-8 chromium-nickel steel the tensile strength is substantially more than doubled. And it is noted that while the tensile strength of my steel is brought to a figure less than 200 K.s.i., that of the 18-8, both examples, is brought to a figure significantly exceeding 200 K.s.i.

Similarly, in the other examples illustrative of the steels of my invention, those of manganese contentswell within a' preferred composition range but somewhat below the manganese content of the most preferred range (Heats 3303-1, 3303-2, 3303-3 and 3305 the tensile strengths are less than doubled by the percent cold-reduction, although in three of the examples the strength had does exceed 200 K.s.i. 198.2 to 209.0 K.s.i. for the one group and 202 to 210 K.s.i. for the other), but is still short of the average tensile strength reached with the 18-8 samples.

And of the various samples of my steel with chromium contents just above those of the most preferred steels of the invention (Heats 3306 and 3307 and those with chromium contents just below the most preferred steels (Heats 331 l-l 3311-2, 3312-1 and 3312-2) (all being well within the broad composition range as well as within certain preferred ranges of my steels) the tensile values are less than doubled with a 65 percent cold-reduction in the case of the group of slightly high chromium contents and just slightly more than doubled in the case of the group of the slightly low chromium contents. But here again, the tensile strengths reached are not as great as those realized with the l8-8 samples (192.1 to 196.6 K.s.i. for the one group and 195.2 to 205.0 K.s.i. for the other, as compared to 202 to 210 K.s.i. for the 18-8 samples).

With a cold-reduction amounting to as much as percent the work-hardening still is acceptable; the yield strength only rises to about 220,000-230,000 p.s.i. and the tensile strength to about 240,000-250,000 p.s.i. As particularly illustrative of the acceptability of the work-hardening had in my steel, the mechanical properties of 0.2 percent yield strength, tensile strength, percent elongation in 2 inches and Rockwell hardness had with strip samples of my preferred steel (Heats 3313-1, 3313-2, 3315 and 3320 of table "(a for differing amountsof cold-reduction are given below in table 111.

TABLE III Cold-reduction and resultant mechanical properties of strip samples of heats 3313-1, 3313-2, 3315 and 3320 Percent Percent cold- 2% Y S Tensile, elong. Rockwell Heat No. reduction K s.i. K s.i. in 2 hardness 0. 0 40. 8 96. 4 60. 5 B76. 0 5. 7 55. 6 100. 5 55. 5 B85. 0 18. 0 105. 2 123. 6 28. 5 C30. 0 3313-1 34. 7 135. 1 153. 2 9. 5 C36. 5 50. 1 159. 2 178. 7 5. 5 C41. 0 65. 0 184. 5 198. 0 3. 0 C42. 0 1 80. 0 204. 0 217. 0 2.0 C43. 5 0. 0 40. 0 94. 9 62. 0 B74. 5 4. 9 56. 4 97. 1 54. 5 B86. 0 20. 8 106. 2 122. 3 26. 0 C30. 0 3313-2 35. 1 130. 7 148. 5 11. 0 C35. 0 51. 0 156. 1 176. 0 5. 0 C40. 5 65. 0 171. 7 192. 0 3. 0 C42. 0 1 80. 0 190. 0 204. 0 2. 0 C43. 5 0. 0 42. 7 96. 2 59. 0 B76. 0 5. 3 56. 6 97. 2 52. 5 B83. 0 21. 2 110.0 126. 2 24. 5 C28. 5 3315 36. 0 137. 2 155. 7 10. 5 C35. 5 51.0 159. 5 179. 7 5. 5 C39. 5 65. 7 174.6 193. 2 4. 0 C41. 0 1 80. 0 183. 0 200. 0 3. 0 C42. 5 0. 0 46. 3 98. 2 55. 0 B79. 0 6. 1 66. 6 102. 0 46. 0 B90. 5 23. 2 117. 1 133. 2 19. 0 C31. 5 3320 35. 2 137. 6 156. 5 10. 5 C36. 0 49. 7 153. 4 178. 2 7. 0 C39. 5 64. 7 173. 2 188. 7 5. 5 C41. 0 1 80. 0 182. 0 197. 0 4. 0 C42. 5

1 Extrapolation.

to level off at about 205,000 p.s.i. yield strength and 220,000

p.s.i. tensile strength. ln my steel, therefore, sheet, strip and the like may be hot-ro1led to a thickness of some 0.100 inch and then, following annealing, cold-rolled to a thickness of 0.015 inch without necessity for an intermediate anneal during cold-rolling, and all at minimum mill cost.

Thus, it will be seen that 1 provide a stainless steel in which the various objects and advantages hereinbefore set forth are successfully achieved. In the steels of my invention there are achieved savings in chromium and nickel (the nickel content being only about one-half of that required in the well-known 18-8 chromium-nickel grade as noted above) an yet the hardness developed in cold-working is no greater, infact, slightly less. Moreover, as a result of a lowering of the nickel content there is a greater solubility for carbon with less likelihood for weld sensitivity, that is, sensitivity of the steel to carbide precipitation in the heat-affected area with resultant chromium impoverishment and susceptibility to intergranular attack.

The steels of my'invention are produced at minimum cost through savings in expensive alloying additions (chromium and nickel as noted) and through savings in cold-working costs as a result of eliminating the intermediate annealing operation commonly required with the types 201 and 301.

My steel in the form of cold-rolled sheet and strip and in the form of cold-drawn wire is offered to the trade in the annealed condition or annealed, pickled and temper-rolled condition or in a bright-annealed or brightannealed and temper-rolled condition. it well lends itself to a variety of working and forming operations such as bending, pressing, drawing, deep-drawing and spinning, as well as a variety of machining operations such as shearing, cutting, drilling, tapping, and the like, as in the fabrication of a host of articles of ultimate use. It may be brazed and welded for some applications without necessity for subsequent anneal.

in short, the steels of my invention are blessed by the workability of the known type 302 (18-8 chromium-nickel stainless steel). And these steels may be made at a significantly lower cost, a cost comparing favorably with the type 202 and with the type 201 in the ingot and less costly in the form of coldrolled sheet and strip and cold-drawn wire, this because of the short routing through the mill. And the cold-forming properties and corrosion-resisting characteristics of my steel compare favorably with those of the type 302, being suited to the fabrication, as by pressing, bending and drawing ofa variety of articles and products of ultimate use, illustratively, automobile trim and wheel covers; kitchen sinks, trim and bar equipment; architectural applications, both indoor and outdoor; foodhandling equipment for domestic and restaurant uses such as utensils, hollow-ware and steam table pans; washingmachine tubs; bulk milk tanks and other dairy equipment; laundry and dry cleaning equipment; as well as a host ofsirnilar uses.

Since many embodiments of my invention will occur to those skilled in the art to which the invention relates, and since many modifications of the present embodiments likewise will occur to the skilled, it is to be understood that all matter described herein is to be interpreted as illustrative and not by way of limitation.

lclaim:

11. Stainless steel of low work-hardening rate essentially consisting of carbon up to 0.15 percent manganese 3 to percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium percent to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.04 to 0.4 percent with a nitrogen content of at least 0.07 percent for the maximum values of carbon, manganese and nickel and with a chromium content of about 19 percent and remainder substantially all iron.

2. Stainless steel of low work-hardening rate essentially consisting of carbon up to 0.12 percent, manganese 5 to 8.5 percent, phosphorus not exceeding 0.06 percent, sulphur not ex ceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 17.5 percent, nickel 3.5 to 6 percent, copper 0.75 to 2,5 percent, nitrogen 0.04 to 0.1 percent, and remainder substantially all iron.

3. Stainless steel of low work-hardening rate essentially consisting of carbon 0.04 to 0.15 percent, manganese 3 to 10 percent, phosphorus not 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 percent to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.04 to 0.4 percent with a minimum nitrogen content of 0.07 percent where manganese is about 10 percent and chromium about 19 percent, and remainder substantially all iron.

4. Stainless steel of low work-hardening rate essentially consisting of carbon up to about 0. 15 percent, phosphorus 3 percent to 7.5 percent, phosphorus not exceeding 0.06 percent, sulfur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.25 percent, and remainder substantially all iron.

5. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon up to about 0.15 percent, manganese 7.5 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.04 percent to 1 percent, chromium 17 to 19 percent, nickel 4 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.4 percent with a minimum nitrogen content of 0.08 percent for manganese about 10 percent and chromiurn about 19 percent, and remainder substantially all iron.

6. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.1 1 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper l to 4 percent, nitrogen 0.07 to 0.12 percent, and remainder substantially all iron.

7. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.15 percent, manganese 5.5 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, copper 1 to 3.5 percent, nitrogen 0.08 to 0.25 percent, and remainder substantially all iron.

8. Stainless steel substantially free of delta-ferrite and low work-hardening rate essentially consisting of carbon about 0.07 to 0.11 percent, manganese about 5.5 to 6 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon about 0.4 to 0.75 percent chromium about 16.25 to 17.25 percent, nickel about 3.5 to 4.5 percent, copper abut 2.5 to 3.25 percent nitrogen about 0.08 percent to 0.12 percent, and remainder substantially all iron.

9. Hot-rolled stainless steel sheet, strip, wire, and the like of low worlohardening rate essentially consisting of carbon up to about 0.15 percent, manganese 3 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.l5 to 1 percent, chromium 15 to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.25 percent with a minimum nitrogen content of0.08 percent where manganese is about 10 percent and chromium about 19 percent, and remainder substantially all iron.

10. Hot-rolled stainless steel sheet, strip, wire, and the like substantially free of delta-ferrite and of low w0rk-hardening rate essentially consisting of carbon 0.04 to 0. 15 percent, manganese 5.5 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, copper l to 3.5 percent, nitrogen 0.08 percent to 0.25 percent, and remainder substantially all iron.

11. Cold-worked stainless steel sheet, strip, wire, and like products essentially consisting of carbon 0.04 to 0.1 1 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper l to 4 percent, nitrogen 0.05 to 0.12 percent, and remainder substantially all iron.

l2. Cold-rolled stainless steel sheet, strip, and like products substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.11 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper l to 4 percent, nitrogen 0.07 to 0.l2 percent, and remainder substantially all iron.

13. Cold-rolled stainless steel sheet, strip and like products of about 0.1 15 to 0.032 inch thickness having a 0.2 percent yield strength not exceeding 220,000 to 230,000 p.s.i. and a tensile strength not exceeding 240,000 to 250,000 p.s.i. for a cold-reduction of at least about 60 percent without intermediate annealing during cold-rolling, said sheet, strip and the like essentially consisting of carbon up to about 0.15 percent, manganese 3 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 003 percent, silicon 0.15 to 1 percent, chromium 15 to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.04 to 0.4 percent with a minimum nitrogen content of 0.07 percent where manganese is about 10 percent and chromium about 19 percent and remainder substantially all iron. 

2. Stainless steel of low work-hardening rate essentially consisting of carbon up to 0.12 percent, manganese 5 to 8.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 17.5 percent, nickel 3.5 to 6 percent, copper 0.75 to 2,5 percent, nitrogen 0.04 to 0.1 percent, and remainder substantially all iron.
 3. Stainless steel of low work-hardening rate essentially consisting of carbon 0.04 to 0.15 percent, manganese 3 to 10 percent, phosphorus not 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 percent to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 PERCENT, nitrogen 0.04 to 0.4 percent with a minimum nitrogen content of 0.07 percent where manganese is about 10 percent and chromium about 19 percent, and remainder substantially all iron.
 4. Stainless steel of low work-hardening rate essentially consisting of carbon up to about 0.15 percent, phosphorus 3 percent to 7.5 percent, phosphorus not exceeding 0.06 percent, sulfur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.25 percent, and remainder substantially all iron.
 5. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon up to about 0.15 percent, manganese 7.5 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.04 percent to 1 percent, chromium 17 to 19 percent, nickel 4 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.4 percent with a minimum nitrogen content of 0.08 percent for manganese about 10 percent and chromium about 19 percent, and remainder substantially all iron.
 6. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.11 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper 1 to 4 percent, nitrogen 0.07 to 0.12 percent, and remainder substantially all iron.
 7. Stainless steel substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.15 percent, manganese 5.5 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, copper 1 to 3.5 percent, nitrogen 0.08 to 0.25 percent, and remainder substantially all iron.
 8. Stainless steel substantially free of delta-ferrite and low work-hardening rate essentially consisting of carbon about 0.07 to 0.11 percent, manganese about 5.5 to 6 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon about 0.4 to 0.75 percent chromium about 16.25 to 17.25 percent, nickel about 3.5 to 4.5 percent, copper abut 2.5 to 3.25 percent nitrogen about 0.08 percent to 0.12 percent, and remainder substantially all iron.
 9. Hot-rolled stainless steel sheet, strip, wire, and the like of low work-hardening rate essentially consisting of carbon up to about 0.15 percent, manganese 3 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.05 to 0.25 percent with a minimum nitrogen content of 0.08 percent where manganese is about 10 percent and chromium about 19 percent, and remainder substantially all iron.
 10. Hot-rolled stainless steel sheet, strip, wire, and the like substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.15 percent, manganese 5.5 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 16 to 18 percent, nickel 3.5 to 5.5 percent, cOpper 1 to 3.5 percent, nitrogen 0.08 percent to 0.25 percent, and remainder substantially all iron.
 11. Cold-worked stainless steel sheet, strip, wire, and like products essentially consisting of carbon 0.04 to 0.11 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper 1 to 4 percent, nitrogen 0.05 to 0.12 percent, and remainder substantially all iron.
 12. Cold-rolled stainless steel sheet, strip, and like products substantially free of delta-ferrite and of low work-hardening rate essentially consisting of carbon 0.04 to 0.11 percent, manganese 3 to 7.5 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.4 to 1 percent, chromium 15 to 18 percent, nickel 3.5 to 5.5 percent, copper 1 to 4 percent, nitrogen 0.07 to 0.12 percent, and remainder substantially all iron.
 13. Cold-rolled stainless steel sheet, strip and like products of about 0.115 to 0.032 inch thickness having a 0.2 percent yield strength not exceeding 220,000 to 230,000 p.s.i. and a tensile strength not exceeding 240,000 to 250,000 p.s.i. for a cold-reduction of at least about 60 percent without intermediate annealing during cold-rolling, said sheet, strip and the like essentially consisting of carbon up to about 0.15 percent, manganese 3 to 10 percent, phosphorus not exceeding 0.06 percent, sulphur not exceeding 0.03 percent, silicon 0.15 to 1 percent, chromium 15 to 19 percent, nickel 3.5 to 6 percent, copper 0.5 to 4 percent, nitrogen 0.04 to 0.4 percent with a minimum nitrogen content of 0.07 percent where manganese is about 10 percent and chromium about 19 percent and remainder substantially all iron. 